Patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches are well established in the biological art and described i.e. in "Pfluegers Archiv"/European Journal of Physiology 391 (1981) pages 85-100. The science and technology of patch-recording electrodes is described in "Single Channel Recording" (B. Sakmann and E. Neher, eds.), Plenum Press, New York and London (1983), pages 53 to 68. A copy of these publications is submitted with this application. A measuring system for exceedingly weak currents useful for patch recording is described in U.S. Pat. No. 4,510,442 issued Apr. 9, 1985 and incorporated by reference.
Patch pipettes are generally made by a three-stage process: Pulling a pipette, coating of its shank with a silicone resin, such as "Sylgard"(trademark of Dow Corning Corp.), and heat polishing of the pipette tip. The present invention relates to said second and third process steps.
The "Sylgard" coating is employed for the purpose of reducing the pipette-bath capacitance and to form a hydrophobic surface. In the known process, this step is performed by using a coating jig comprising a clamp for positioning the pipette, and a nichrome heating coil surrounding the shank of the micropipette and used to cure the coating which had been previously applied. Generally, the coating and the control of the curing are effected with the aid of a microscope with a low power objective.
A peculiarity of uncured "Sylgard" is that a very fine film of this resin tends to creep along the glass surface of the pipette for several millimeters, e.g. to the electrode tip. Since seals of very high resistance as desired for patch recording form only to clean glass, this film must be removed what is effected by burning it off in the third, the heat polishing step. Polishing the pipette tip also prevents damage to the membrane by sharp tip edges.
Polishing is usually done on the stage of a compound microscope under observation with a relatively high power, long working distance objective. The polishing assembly includes a V-shaped, electrically heatable filament and means comprising a tube to direct an air stream to the filament. The air stream is used to generate a steep thermal gradient which confines the polishing action to the very tip of the electrode.